The goal of this project is to elucidate the function of the atrophin protein, mutations of which underlie the neurodegenerative disease dentatorubral-palliudoluysin atrophy (DRPLA). These mutations are expansions of a polyglutamine repeat motif (coded by CAG trinucleotide repeats in the mRNA) within the protein, making DRPLA one of several known "glutamine repeat disorders." In this group of neurodegenerative diseases, an expansion of polyglutamine repeat in a number of different proteins confers the various disease phenotypes. However, in spite of the relatively restricted patterns of differential cell death in DRPLA and the other disorders, the gene products are widely distributed in both the central nervous system and peripheral tissues, and not their normal functions and mechanisms of disease are largely unknown. The DRPLA gene product atrophin has a number of advantages as a model protein for study; it is hydrophilic, of moderate size, and contains a number of intriguing peptide motifs which may be important in its function. This study will examine the function of atrophin through four specific aims. First, antibodies will be generated against purified atrophin, bacterial fusion proteins, and small synthetic peptides. These regents will be used to probe the regional, cellular, and subcellular localizations of atrophin in brain. The focus of the project, however, will be the identification of proteins that interact with atrophin, using yeast two hybrid screening and affinity purification techniques. The effect of expansion of polyglutamine repeat on any identified interactions will then be assessed. A focus on protein-protein interactions is critical while evaluating the function of atrophin, as alterations in which interactions due to the polyglutamine repeat expansion may be involved in the pathogenesis of DRPLA. Finally, the effects of differential alternative splicing of the atrophin gene on atrophin protein-protein interactions will be examined. Hereditary disorders such as DRPLA and the other glutamine repeat diseases are of particular interest of neurologists, as identification of the mechanism of neurodegeneration in these hereditary disorders will likely shed light on similar mechanisms in the more common acquired neurodegenerative diseases such as Alzheimer's disease, amyotrophic lateral sclerosis, and Parkinson's disease. During the course of this research, sponsored by Morgan Sheng MBBS, PhD, the candidate expects to be trained in the cutting edge techniques of molecular genetics and protein biochemistry that will empower him to pursue a productive career in molecular neurology.